1. Field of the Invention
The present invention relates to optical ion sensors, including fluorescence optical ion sensors for use in liquid media in the fields of biology, biotechnology, chemistry, medicine, etc. The present invention provides for optical ion sensors that may be attached to dry hydrophilic or hydrophobic surfaces so as to allow continuous sensing. The optical sensors of the present invention may be sterilized and stored for extended periods of time before use.
2. Background of the Invention
Optical ion sensors, and specifically optical fluorescence ion sensors, rely on a chemical interaction of the ion to be analyzed with an indicator that changes its optical properties upon interaction. Generally this indicator will be a fluorescent molecule or fluorescent dye. In order to be considered a sensor (and not an assay) the indicator must be immobilized so as to keep the indicator in the field of view of the interrogation electronics, and to supply a relatively constant concentration of the indicator in the sensing area.
An indicator may be immobilized on the surface or in the bulk of a sensor. While surface immobilization ensures easy access of the ions to the indicator, the signal is usually very weak due to the extremely low thickness of the sensing layer. In addition, in complex environments, a background fluorescence often exists, which can interfere with a fluorescence measurement. A natural solution is to increase the signal intensity by immobilizing the dye in the bulk of a semi-permeable membrane, thus increasing the total amount of dye in the observation path. The membrane should be “transparent” to analyzed ions, but it should not allow the indicator molecule to leave it. The first requirement is often achieved by use of a hydrophilic (hydrogel) membrane. The second requirement is achieved by some form of entrapment (physical or chemical) of the indicator in the bulk of the polymer material.
In addition to immobilization of the indicators in a membrane material, the sensor also needs to be positioned and held by some means in front of the detection optoelectronics so as to allow for unobstructed, constant measurement of the ions in solution. Previously, this attachment has achieved by use of a mechanical holder (i.e. mesh) over the sensor. This method, however, allows solution to flow behind the sensor, thereby interfering with the optical measurement and in some cases moving the sensor out the optical pathway. U.S. Pat. No. 5,114,676 provides a pH sensor with a fluorescent indicator which may be covalently attached to a particle or to a microcrystalline cellulose fiber. The majority of the particle/indicator is imbedded within a hydrogel layer that is applied over a thermoplastic layer. The pH sensor is applied to the tip of an optical waveguide.
There exists however, a need for an optical ion sensor that can be immobilized, either permanently or semi-permanently, on dry hydrophilic or hydrophobic materials, (e.g., bioreactors, shake flasks, T-flasks, microwell plates, etc.) to allow for an unobscured light path between the interrogation optoelectronics and the sensing layer. The present application fulfills this need.